USGS Professional Paper 1697 - Alaska Resources Library

42 Metallogenesis and Tectonics of the Russian Far East, Alaska, and the Canadian Cordillera
was an unknown subduction zone (UNK). In the southern
Canadian Cordillera today, the Sicker arc is defined by the
Sicker Group, which consists of Late Devonian arc-related
volcanic and sedimentary strata, having a U-Pb zircon age
of 367 Ma, and coeval intrusions (Muller, 1980; Parish and
McNicoll, 1992). Occurring in the Alexander sequence (AX)
was the Mount Sicker metallogenic belt of kuroko massive
sulfide deposits, which formed in the subduction-related,
short-lived Sicker arc. Insufficient data exist to ascertain the
relative positions of the Wrangellia superterrane (WRA) and
associated subduction zone. On the basis of paleomagnetic,
geologic, geochronologic, and faunal data, the Wrangellia
superterrane (Alexander sequence, AX) may have been
derived from the Russian platform (Baltica) in the Barents
Sea region (Bazard and others, 1993, 1994) or possibly from
Australia (Gehrels and Saleeby, 1987).
Metallogenic Belt Formed During Collision
Yaroslavka Metallogenic Belt of Fluorite and Sn
Greisen Deposits (Belt YA), Southern Part of
Russian Southeast
The Yaroslavka metallogenic belt of fluorite and Sn
greisen deposits (fig. 16; tables 3, 4) occurs in the southwestern
part of the Primorye Province of the Russian southeast
(Ryazantseva, 1998). The deposits occur in numerous early
W
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Paleozoic granitoid plutons that intrude Cambrian clastic and
limestone units in the Vosensenka continental-margin arc terrane
of the Khanka superterrane. The major fluorite greisen
deposit is at Voznesenka-II; the major Sn greisen deposit is at
Yaroslavka (table 4) (Nokleberg and others 1997a,b, 1998).
Voznesenka-II Fluorite Greisen Deposit
The major Voznesenka-II fluorite greisen deposit (fig. 19)
(Androsov and Ratkin, 1990; Ryazantzeva, 1998) consists
of fluorite that occurs above the apex of a 1.5 km-wide Late
Cambrian intrusion of lithium-fluorine alaskite granite with
Rb-Sr isotopic ages of about 512-475 Ma. The fluorite is interpreted
as forming from metasomatic replacement and alteration
of Early Cambrian, black organic limestone to greisen
along a north-south-trending fault into which the alaskite granite
intruded. An aggregate of muscovite and fluorite occurs
at the periphery of the ore zone, whereas the greisen occurs
in the middle of the zone. The greisen is often brecciated into
fragments of mica and fluorite, fluoritized limestone, greisen,
and greisenized granite, which are cemented by an aggregate
of quartz, topaz, and micaceous-fluorite. The deposit is very
large and contains an estimated 450 million tons fluorite ore
averaging 30 to 35 percent CaF2. The Voznesenka-II deposit
has been mined since 1960’s, is the sole producer of Russian
fluorspar, and is currently one of the largest fluorine producers
in the world.
The formation of the greisen fluorspar deposits is interpreted
as related to intrusion of Late Cambrian leucogranite
0 m
200 m
400 m
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Quaternary deposits
Basic and intermediate
dikes
Greisenized granite
Fluoritized limestone
Fluorite ore
Slate
Limestone
Tectonic fault and zone
Contact
0 120 m
Figure 19. Voznesenka II F greisen deposit, Yaroslavka metallogenic belt, Russian Southeast. Schematic
cross section through Glavnoe deposit. Adapted from Androsov and Ratkin (1990) and Ryazantzeva
(1998). See figure 16 and table 4 for location. Elevations below sea level.